The present invention relates to a spacer expander of an oil ring utilized for an internal combustion engine and more particularly to a spacer expander constructed from a strip of metal and composed of a split annular spring body and lugs projected axially from the body to hold a side rail in contact with the cylinder wall of the engine.
A spacer expander is generally assembled with a pair of side rails into an oil ring. The spacer expander comprises a split annular spring body when its opposite ends are in contact. The body is formed with a plurality of alternate corrugations to provide a radial expansive force. The inward corrugations are provided with lugs inclined slightly in a direction radially inward of the body. The lugs form a conical surface to engage the inner radial face of the side rail and bias the rail outwardly against the cylinder wall of the engine. The spacer expander is manufactured by blanking a strip of steel, so that the thickness of the lug is uniform and similar to that of the body.
The spacer expander as disclosed in U.S. Pat. No. 3,140,096 is provided with lugs having no uniform thickness. The lug extends axially from the circular body and is chamfered on its outward face to form a conical surface together with the others. The angle of chamfer is in the range of 7 degrees. The lug is also similar in thickness at its root portion to the body.
The known spacer expander is formed with lugs each being the same in cross-sectional thickness at least at the root thereof as the body, thus the root is too rigid to elastically bend. When a part of the lugs are inwardly biased by the side rail, the lugs cause the humps connected therewith to displace inwardly therewith. This leads to an increase of oil consumption in an internal combustion engine under an engine brake operation in which the piston easily swings around the piston pin and easily inclines to the cylinder. Upon the inclination of the piston, one of the upper and lower side rails strongly pushes a part of the lugs inwardly. Then, the body is displaced inwardly to permit the separation of the outer end of the other side rail from the cylinder wall, resulting in a reduction of the oil scraping effect because the other side rail is separated from the cylinder wall and free from oil scraping. The reduction in the oil scraping effect causes a problem of more excessive oil consumption than normally need. Especially during the engine braking, piston readily oscillates whereby the oil consumption increases much more.
On the other hand, a thicker body is required so that a sufficient radial expansive force can be exerted on the side rail in a manner such that the side rail is caused to follow the inner surface of the cylinder at high speed operations when the cylinder is somewhat distorted. However, the more the thickness of the spacer expander is thickened, the more the oil consumption increases during engine braking.
An object of the present invention is to provide an improved spacer expander by which the side rail is always in operative contact with the inner surface of the cylinder even when the piston inclines to the cylinder at engine brake running.
Another object of the present invention is to provide an improved spacer expander by which the side rail well follows the inner surface of the cylinder even when the cylinder is deformed at high speed running.
A further object of the present invention is to provide an improved spacer expander with a thickness to exert a sufficient radial expansive force on the side rail.
A still further object of the present invention is to provide an improved spacer expander capable of reducing the oil consumption at engine brake running.
According to the present invention, the improved spacer expander is constructed from a strip of metal to form a split annular shaped spring body when its opposite ends are in contact and assembled with a single or double side rails into an oil ring assembly. The body is similar in cross-sectional thickness to the original strip of metal and formed with a plurality of lugs for bearing engagement with the inner radial face of the side rail. The lug is thinner in cross-sectional thickness at least at its root portion than the body so that it is elastically easily bendable when it is inwardly biased by the side rail. The lug may be thinned uniformly or partly to have its root portion thinner than the body. The body can have a thickness required to exert a sufficient radial expansive force on the side rail and cause the side rail to follow the inner surface of the cylinder at high speed running in which the cylinder is distorted. Machining is available for manufacturing a spacer expander with uniformly or partly thinned lugs after press-working of a steel strip with a uniform thickness. However, it is preferable to eliminate the machining by utilizing press-working of the off-shaped drawn steel strip having beforehand a thinned section for the thin root portion.
In a preferred embodiment , the annular body is radially corrugated to form the inwardly extending humps and outwardly extending humps. Each inwardly extending hump is formed at its upper and lower crest with upper and lower lugs of which the cross-sectional thickness is thinner than that of the hump. The body is assembled with upper and lower side rails and set in a piston ring groove in a piston. When the piston inclines to the cylinder wall, either of the upper and lower side rails biases a part of the lugs inwardly. The thin lug can elastically bend independently from the body whenever it is inwardly biased by the rail, so that the body remains unmoved. This offers an advantage in that the upper and lower side rails are always in contact with the cylinder wall, even when the piston inclines to the cylinder wall. Therefore, whenever the piston oscillates, during engine braking, upper and lower side rails are always in contact with the internal surface of the cylinder and perform a sufficient oil scraping operation, which consequently limits increases in oil consumption. The thickness of the body or spacer expander can be determined in a manner that it exerts a sufficient radial expansive force on the upper and lower side rails and causes them to follow the cylinder wall at high speed running in which the cylinder is deformed.
Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawings.